pressure is only 0.8 bar?

0-8 is still ok it is more likely the rads are airlocked turn off rads that are working this should do the trick some boilers have a built in refill otherwise look under the boiler for a flexible silver pipe at one or both ends there will be a tap with either a small black handle or a slot for a screwdriver do not turn anything with a blue red or yellow handle these are the boiler isolation valves

brian
November 2010